Phosphatidylserine and phosphatidic acid are two naturally occurring phospholipid classes. Biochemical and biophysical functions of the phospholipids are well documented and appear to be determined by the composition of phospholipid fatty acid chains. Fatty acid chains with more than two double bonds are generally called highly polyunsaturated fatty acids. Laboratory experiments have shown pharmacological effects of highly polyunsaturated fatty acid-containing phosphatidylserine and phosphatidic acid molecules on enhancing cholinergic neurotransmission.
Due to the difficulty of chemically synthesizing highly polyunsaturated fatty acid-containing phosphatidylserine and phosphatidic acid molecules, chemical extraction and purification of such molecules from bovine brain, particularly the highly polyunsaturated fatty acid-containing phosphatidylserine molecules, is generally practical approach to obtain them. Unfortunately, the risk of bovine spongiform encephalopathy made the use of phosphatidylserine molecules extracted from bovine brain potentially dangerous, and the development of an alternative method to prepare highly polyunsaturated fatty acid-containing phosphatidylserine and phosphatidic acid molecules is desired and lacking. In recent years, new features of phosphatidylserine molecules have been made by phospholipase D-catalyzed transphosphatidylation of egg and soybean phosphatidylcholine and have been used as brain cell nutrients as well. But highly polyunsaturated fatty acid-containing phosphatidylserine and phosphatidic acid molecules are generally lacked in final products.
Fish liver phospholipids contain more than 65% of highly unsaturated fatty acid-containing phosphatidylcholine molecules (less than 5% of phosphatidylserine+phosphatidic acid), and this natural material is considered to be safe for the preparation of highly polyunsaturated fatty acid-containing phosphatidylserine and phosphatidic acid molecules by the phospholipase D-catalyzed transphosphatidylation procedure. Natural phosphatidylcholine can also be readily separated and purified from other phospholipids using chromatographic techniques.